Will testing guarantee that my employees are good?

Nothing can provide a 100% guarantee on the quality of an employee you hire. However, pre-employment, or even post-employment testing, can give you many indicators of how an employee will perform over the course of employment. Testing employees in this way can give them practical experience for the job and allow you to observe how they cope with their duties, both physical and otherwise. Thus, even though there is no guarantee, testing can be immensely beneficial.